I just deleted the question: it's way below our quality standards, had a tremendous amount of down-votes, and was never going to be saved. Feel free to [recalculate your reputation](https://softwareengineering.meta.stackexchange.com/a/2627/8) to get your points back.

I mention that because when you answer a question like that, you're only setting yourself up for pain: the question's going to get closed and deleted, and you're not doing yourself any favors by answering it before it does.

Instead, you just open yourself up for something like what happened: bad question, you leave an answer most people don't like it, and now you've got a negative-scored answer on a question that really wasn't worth anyone's time of day.

And your answer was nothing more than a link to an external resource: even barring the implications of cheating or what-have-you, it's not an answer. From [the FAQ](https://softwareengineering.stackexchange.com/faq):

> Answers that do not fundamentally answer the question may be removed. This includes answers that are …

> * commentary on the question or other answers
* asking another, different question
* “thanks!” or “me too!” responses
* exact duplicates of other answers
* **barely more than a link to an external site**
* not even a partial answer to the actual question

As others have said, people can vote however they like, but in reality, people should've flagged your answer as "not an answer."

Now, if you left that as a *comment*, it wouldn't have been subject to downvotes or have affected your reputation, and would've been perfectly fine. Keep that in mind in the future: if you just want to link to something that might help the OP, just do it as a comment.

To your final question, about whether it's acceptable to revenge down-vote someone who's done you wrong: no, it's not. It'll almost certainly be caught and reversed, and you'll likely wind up getting a message from one of us moderators about it.

And in reality, it wasn't *just* the person who said they down-voted that did it: there were 4 people who did. At least one person had the courtesy to tell you why they did it: why retaliate against them when clearly several people felt the same way about your answer?